1. Field of the Invention
The present invention relates to a method for producing a material for a composite electrode that can be used in particular in an electrochemical battery or in a supercapacitor, and also to the material obtained.
2. Description of the Related Art
Composite electrodes made of a material comprising the active substance and a polymer, having an oxygen mass content of greater than 15%, as binder are known. In particular PEO has been used for batteries of the dry, lithium metal/polymer type. In batteries of the lithium ion or lithium metal/polymer gel type, which contain a liquid electrolyte, polymers other than PEO are used because of the known solubility of PEO in the liquid electrolytes, this being deleterious to the mechanical cohesion of electrode and electrode/current-collector assemblies during impregnation with the liquid electrolyte.
Also known, from D. Guyomard et al., [Solid State Ionics 69, (1994), 222-237], is the preparation of a composite electrode by a method that consists in introducing the active electrode material and carbon black into a solution of PVDF in cyclopentanone, in coating the paste obtained onto a metal foil that can serve as collector, and in evaporating the cyclopentanone solvent. When in contact with a liquid electrolyte in a battery, the composite electrode is impregnated by the electrolyte, which confers ionic conductivity thereon. The electrolyte may be a solution of a lithium salt in a mixture of nonvolatile solvents, for example EC+DEE (ethylene carbonate+diethoxy-ethane) or EC+DMC (ethylene carbonate+dimethyl carbonate). The nonvolatile solvent for the electrolyte acts as plasticizer for the PVDF.
Furthermore, N-M. Choi et al., [J. Power Sources 112, (2002), 61-66] describe the preparation of a composite electrode in which the binder comprises a PMMA polymer and a PVdf or PVdF-HFP polymer. Cathodes containing, as binder, various PMMA/PVdF or PMMA/PVdF-HFP blends are immersed, after their preparation, in an LiPF6 EC/PC solution before being mounted in an electrochemical cell. The binder for the composite electrode material then consists of the polymer blend and a liquid plasticizer.